ΔE 9.0, close: similar, with a visible difference side by side. Typhon Ash is a little darker than IJA Grey Green.
Can I use Typhon Ash instead of IJA Grey Green?
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Typhon Ash is a little darker than IJA Grey Green.
Can I use IJA Grey Green instead of Typhon Ash?
The same difference applies the other way round: IJA Grey Green is a little lighter.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.